Current regulator and method for efficiency improvement of a LED display system
For efficiency improvement of a LED display system including a charge pump and a LED connected to either the voltage input terminal or the voltage output terminal of the charge pump, either one or both of two current regulators are enabled according to a voltage detected from the LED, for establishing a driving current for the LED. When the detected voltage is higher than a threshold, the first one of the current sources is enabled sole. When the detected voltage is lower than the threshold, the second one of the current sources is enabled sole, or both the current sources are enabled, or the current sources are alternatively enabled.
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The present invention is related generally to a Light Emitting Diode (LED) display system and, more particularly, to a current regulator for a LED display system.
BACKGROUND OF THE INVENTIONTherefore, it is desired a circuit and method for efficiency improvement of a LED display system.
SUMMARY OF THE INVENTIONAn object of the present invention is to provide a current regulator and method for efficiency improvement of a LED display system.
According to the present invention, a LED display system includes a charge pump, a LED connected between a voltage input terminal of the charge pump and a node, and a current regulator including a first current source connected between the node and a ground terminal, a second current source connected between the node and a voltage output terminal of the charge pump, and a mode decision circuit connected to the first and second current sources to enable at least one of the first and second current sources for establishing a driving current for the LED.
According to the present invention, a LED display system includes a charge pump, a LED connected between a ground terminal and a node, and a current regulator including a first current source connected between the node and a voltage input terminal of the charge pump, a second current source connected between the node and a voltage output terminal of the charge pump, and a mode decision circuit connected to the first and second current sources to enable at least one of the first and second current sources for establishing a driving current for the LED.
According to the present invention, a method for efficiency improvement of a LED display system including a charge pump and a LED connected between a voltage input terminal of the charge pump and a node comprises detecting a voltage at the node and according thereto, enabling at least one of a first current source connected between the node and a ground terminal and a second current source connected between the node and a voltage output terminal of the charge pump, for establishing a driving current for the LED.
According to the present invention, a method for efficiency improvement of a LED display system including a charge pump and a LED connected between a node and a ground terminal comprises detecting a voltage at the node and according thereto, enabling at least one of a first current source connected between a voltage input terminal of the charge pump and the node and a second current source connected between a voltage output terminal of the charge pump, for establishing a driving current for the LED.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:
Iavg=(I1/2)+(I2/2). [Eq-1]
The duty of the control signal, i.e. the on-time Ton and the off-time Toff, will vary with the input voltage VIN.
While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.
Claims
1. A current regulator for efficiency improvement of a LED display system including a charge pump and a LED connected between a voltage input terminal of the charge pump and a node, the current regulator comprising:
- a first current source connected between the node and a ground terminal;
- a second current source connected between the node and a voltage output terminal of the charge pump; and
- a mode decision circuit connected to the first and second current sources to enable at least one of the first and second current sources for establishing a driving current for the LED.
2. The current regulator of claim 1, wherein the mode decision circuit detects a voltage at the node to enable at least one of the first and second current sources.
3. The current regulator of claim 1, wherein the mode decision circuit enables the first current source sole when a voltage at the node is higher than a threshold, and enables the second current source sole when the voltage at the node is lower than the threshold.
4. The current regulator of claim 1, wherein the mode decision circuit enables the first current source sole when a voltage at the node is higher than a threshold, and enables both the first and second current sources when the voltage at the node is lower than the threshold.
5. The current regulator of claim 1, wherein the mode decision circuit enables the first current source sole when a voltage at the node is higher than a threshold, and provides a control signal to alternatively enable the first and second current sources when the voltage at the node is lower than the threshold.
6. The current regulator of claim 5, wherein the control signal has an on-time during which the first current source is enabled and an off-time during which the second current source is enabled.
7. A current regulator for efficiency improvement of a LED display system including a charge pump and a LED connected between a ground terminal and a node, the current regulator comprising:
- a first current source connected between the node and a voltage input terminal of the charge pump;
- a second current source connected between the node and a voltage output terminal of the charge pump; and
- a mode decision circuit connected to the first and second current sources to enable at least one of the first and second current sources for establishing a driving current for the LED.
8. The current regulator of claim 7, wherein the mode decision circuit detects a voltage at the node to enable at least one of the first and second current sources.
9. The current regulator of claim 7, wherein the mode decision circuit enables the first current source sole when a voltage at the node is higher than a threshold, and enables the second current source sole when the voltage at the node is lower than the threshold.
10. The current regulator of claim 7, wherein the mode decision circuit enables the first current source sole when a voltage at the node is higher than a threshold, and enables both the first and second current sources when the voltage at the node is lower than the threshold.
11. The current regulator of claim 7, wherein the mode decision circuit enables the first current source sole when a voltage at the node is higher than a threshold, and provides a control signal to alternatively enable the first and second current sources when the voltage at the node is lower than the threshold.
12. The current regulator of claim 11, wherein the control signal has an on-time during which the first current source is enabled and an off-time during which the second current source is enabled.
13. A method for efficiency improvement of a LED display system including a charge pump and a LED connected between a voltage input terminal of the charge pump and a node, the method comprising the steps of:
- detecting a voltage at the node; and
- according to the voltage at the node, enabling at least one of a first current source connected between the node and a ground terminal and a second current source connected between the node and a voltage output terminal of the charge pump, for establishing a driving current for the LED.
14. The method of claim 13, wherein the first current source is enabled sole when the voltage at the node is higher than a threshold, and the second current source is enabled sole when the voltage at the node is lower than the threshold.
15. The method of claim 13, wherein the first current source is enabled sole when the voltage at the node is higher than a threshold, and both the first and second current sources are enabled when the voltage at the node is lower than the threshold.
16. The method of claim 13, wherein the first current source is enabled sole when the voltage at the node is higher than a threshold, and the first and second current sources are alternatively enabled by a control signal when the voltage at the node is lower than the threshold.
17. The method of claim 16, wherein the control signal has an on-time during which the first current source is enabled and an off-time during which the second current source is enabled.
18. A method for efficiency improvement of a LED display system including a charge pump and a LED connected between a node and a ground terminal, the method comprising the steps of:
- detecting a voltage at the node; and
- according to the voltage at the node, enabling at least one of a first current source connected between a voltage input terminal of the charge pump and the node and a second current source connected between a voltage output terminal of the charge pump, for establishing a driving current for the LED.
19. The method of claim 18, wherein the first current source is enabled sole when the voltage at the node is higher than a threshold, and the second current source is enabled sole when the voltage at the node is lower than the threshold.
20. The method of claim 18, the first current source is enabled sole when the voltage at the node is higher than a threshold, and both the first and second current sources are enabled when the voltage at the node is lower than the threshold.
21. The method of claim 18, wherein the first current source is enabled sole when the voltage at the node is higher than a threshold, and the first and second current sources are alternatively enabled by a control signal when the voltage at the node is lower than the threshold.
22. The method of claim 21, wherein the control signal has an on-time during which the first current source is enabled and an off-time during which the second current source is enabled.
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Type: Grant
Filed: Oct 26, 2009
Date of Patent: Mar 20, 2012
Patent Publication Number: 20100102731
Assignee: Richtek Technology Corp. (Hsinchu)
Inventors: Shui-Mu Lin (Longjing Township, Taichung County), Tsung-Wei Huang (Taipei), Jien-Sheng Chen (Toufen Town)
Primary Examiner: Douglas W Owens
Assistant Examiner: Thai Pham
Attorney: Rosenberg, Klein & Lee
Application Number: 12/588,702
International Classification: H05B 37/02 (20060101);